Resolving dust and Lyman $\alpha$ emission in a lensed galaxy at the epoch of reionization with JWST/CANUCS

Markov, Vladan (author), Bradač, Maruša (author), Rihtaršič, Gregor (author), Judež, Jon (author), Martis, Nicholas S. (author)

Context. Lyman ▫$\alpha$▫ (Ly▫$\alpha$▫) emission is highly sensitive to dust and neutral hydrogen and is believed to be suppressed in dusty or hydrogen-rich galaxies – especially during the epoch of reionization (EoR). Yet, moderately dusty Ly▫$\alpha$▫ emitters (LAEs) are observed at this epoch, suggesting that complex interstellar medium (ISM) geometries and feedback-driven outflows facilitate Ly▫$\alpha$▫ escape. Aims. We investigated the dust, gas, and stellar properties of the gravitationally lensed LAE HCM 6A at ▫$z = 6.5676$▫ to characterize its multiphase ISM structure and the physical conditions that regulate Ly▫$\alpha$▫ escape. Methods. We combined JWST/NIRISS slitless spectroscopy, HST+JWST/NIRCam imaging, and JWST/NIRSpec slit spectra from the CANUCS program. Using a customized BAGPIPES spectral-energy-distribution-fitting framework with a flexible attenuation law, we derived spatially resolved stellar, nebular, and dust properties on integrated (▫$\approx$▫1 kpc), slit-level (▫$\approx$▫0.1 kpc), and pixel-level (▫$\approx$▫25 pc) measurements, thanks to strong lensing with a magnification of ▫$\mu \approx 8.3 - 9.1$▫. A high-quality Ly▫$\alpha$▫ map from SLEUTH, a tool for extracting spatially resolved emission-line maps from slitless spectroscopy, traces the spatial distribution of Ly▫$\alpha$▫ emission. Results. We measure an unlensed stellar mass of log ▫$M\ast = 8.3 - 8.4$▫ and an intrinsic UV magnitude of ▫$M_{\text{UV}} = -19.8 \pm 0.1$▫. Slit-level measurements show that the oldest, most massive region (S1) is moderately dusty with consistent stellar (▫$A_V, \beta$▫) and nebular (▫$A_V ^{\text{B}}$▫, line-emission) indicators, implying a uniform ISM geometry, while the dust tracers of the youngest region (S3) are highly mismatched, revealing a complex, feedback-shaped multiphase ISM. Ly▫$\alpha$▫ emission arises primarily from S3. Pixel-level maps reveal a dust-cleared central clump (C3) where Ly▫$\alpha$▫ emerges, encircled by dustier outskirts, consistent with a very recent (▫$\lesssim$▫10 Myr) starburst that created Ly▫$\alpha$▫ escape channels. Next, slit-level maps show Calzetti-like attenuation curves with a UV bump that increases with stellar age and decreases with ▫$V$▫-band ettenuation (▫$A_V$▫), with a tentative detection of a UV bump in S1 at ▫$\sim$▫25% of the Milky Way amplitude. Pixel-level maps reveal that both the curve slope (▫$S$▫) and the UV bump (▫$B$▫) peak in the region between two clumps (C1 and C2), indicating dust-grain processing in a merger-driven starburst. Conclusions. Our observations provide a uniquely detailed, spatially resolved view of a moderately dusty LAE at the EoR, demonstrating how the interplay between multiphase ISM geometry and feedback governs Ly▫$\alpha$▫ escape. Constraining some key quantities requires fully resolved spectroscopy, which future JWST/NIRSpec integral field unit observations will provide.

• Language: English
• Keywords: galaxies, galaxy evolution, redshift, dust, extinction
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FMF - Faculty of Mathematics and Physics
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: 13 str.
• Numbering: Vol. 708, art. no. A236
• PID: 20.500.12556/RUL-181941
• UDC: 524.8
• ISSN on article: 1432-0746
• DOI: 10.1051/0004-6361/202558580
• COBISS.SI-ID: 275637507
• Publication date in RUL: 20.04.2026

Record is a part of a journal

• Title: Astronomy & astrophysics
• Shortened title: Astron. astrophys.
• Publisher: EDP Sciences
• ISSN: 1432-0746
• COBISS.SI-ID: 392577

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: galaksije, razvoj galaksij, rdeči premik, medzvezdni prah, ekstinkcija